Lisa Jackson, the former administrator of the US Environmental Protection Agency and Apple's vice president for environmental initiative, wrote in a letter: "We feel the responsibility to consider everything we do in order to reduce our impact on the environment. This means using greener materials and constantly inventing new ways to conserve precious resources.

We want to leave the world better than we found it. We’re proud of our progress but we know we have much more to do. http://t.co/iHzF9rUnx1

Apple said its carbon footprint in 2013 was 33.8 million metric tonnes of greenhouse gas emissions in 2013, or around 5 percent of the United Kingdom's annual CO2 emissions for the same year. Around three-quarters of the emissions come from manufacturing. "We believe climate change is real. And that it's a real problem," the company's website now says.

The company said its new HQ being built in Cupertino, California, will use 30 percent less energy than an equivalent building, and will be home to around 7,000 trees. It also highlighted a decrease in the material required to make its products—the new iPad Air uses nearly one-third less material, by weight, than the original iPad.